Turbine engine nozzle

ABSTRACT

A convergent/divergent nozzle for a gas turbine engine has a throat portion of non-constant radius of curvature varying from an upstream high value to an intermediate low value and then to a downstream high value.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation of U.S. patent application Ser. No. 10/614,632,filed Jul. 7, 2003. and also entitled “Turbine Engine Nozzle.”

U.S. GOVERNMENT RIGHTS

The invention was made with U.S. Government support under contractN00019-02-C-3003 awarded by the U.S. Navy. The U.S. Government hascertain rights in the invention.

BACKGROUND OF THE INVENTION

This invention relates to gas turbine engines, and more particularly toconvergent/divergent exhaust nozzles for gas turbine engines.

A well developed art exists in the field of turbine engine nozzles. U.S.Pat. No. 6,398,129 discloses an exemplary prior art nozzle. Thatexemplary nozzle is an axisymmetric nozzle having an array of flappairs: a convergent flap upstream and a divergent flap downstream. Thedivergent flaps may be articulated through a variety of orientationsassociated with modes of the engine. The exemplary divergent flapincludes, in longitudinal section, a continuously curving convexupstream portion of a given radius of curvature and one or more straightportions downstream. During articulation of the flap between modes, theinstantaneous aerodynamic throat of the nozzle will occur at a locationalong the upstream portion.

BRIEF SUMMARY OF THE INVENTION

One aspect of the invention involves an exhaust nozzle for a gas turbineengine. A first portion has an interior surface converging in adownstream direction. A second portion has an interior surfacedownstream of the interior surface of the first portion. The first andsecond portions may each comprise a circumferential array of flaps. Eachflap in the second portion may be coupled to the first portion forarticulation through a range of mode orientations. The interior surfaceof the second portion along each flap has a central longitudinal radiusof curvature that from upstream to downstream has: a first value along afirst flap portion; at least a second value, less than the first valueand between (inclusively unless noted) 0.25 inch and 1.0 inch along asecond portion; and at least a third value, less than the first value,and between 5.0 inches and 10.0 inches along a third portion.

In various implementations, the radius of curvature may be essentiallyinfinite along a fourth portion downstream of the third portion. Theradius of curvature may be essentially infinite along the first portion.The radius of curvature may continuously increase from a low of between0.25 inch and 5.0 inches to a high of between 8.0 inch and 14.0 inches.The continuous increase may be smooth or stepwise occur over alongitudinal span of between 2.0 inches and 3.0 inches. Saidlongitudinal span may at least partially overlap the second and thirdportions. The range of orientations may extend between a low modeorientation wherein a ratio of an exit area to a throat area is between1.05:1 and 1.5:1 and a high mode orientation wherein the ratio is largerthan in the low mode and between 1.3:1 and 2.0:1. The ratio may bebetween 1.1:1 and 1.3:1 in the low mode and 1.4:1 and 1.5:1 in the highmode. Between the low and high mode orientations, a throat radius maychange by less than 0.5%. That change may be less than 0.2%. Each flapmay be pivotably coupled to the first portion for rotation about anassociated hinge axis during transition between low and high modes. Thehinge axis may have a first radial distance from a centerline of thenozzle. The nozzle second portion may have a throat having a secondradial distance from the centerline and a first longitudinal distancefrom the hinge axis. A ratio of the first longitudinal distance to alongitudinal flap length from the hinge axis to an outlet end is between0.05:1 and 0.20:1.

Another aspect of the invention involves an exhaust nozzle for a gasturbine engine including an upstream portion having a number ofcircumferentially arrayed first flaps and an interior surface convergingin a downstream direction. The downstream portion may include a numberof circumferentially arrayed second flaps each hinged relative to anassociated one of the first flaps. The downstream portion may include adownstream outlet and an interior surface downstream of the interiorsurface of the upstream portion. A longitudinal profile of thedownstream portion interior surface has an essentially straight firstportion. A convex second portion is downstream of the first portion andhas a continuously increasing radius of curvature. The surface may besmooth and the increase may be smooth or stepwise. An essentiallystraight third portion is downstream of the second portion.

In various implementations, the nozzle may include a number ofcircumferentially arrayed third flaps, each outboard of and hingedrelative to an associated one of the second flaps. The radius ofcurvature of the second portion may vary from an upstream value ofbetween 0.25 inch and 0.5 inch to a downstream value of between 8.0inches and 14.0 inches over an axial span of at least 2.0 inches.

Another aspect of the invention relates to a convergent/divergentaxisymmetric exhaust nozzle for a gas turbine engine. There is a hingepivot at the juncture of where the convergent portion and the divergentportion of the nozzle meet. The convergent and divergent portions eachinclude a number of circumferentially spaced axially extending flaps. Aradius throat has a surface exposed to the working medium of the engineand is located downstream of the hinged pivot. The surface of theradiused throat is defined by a convex curvature formed on the flaps ofthe divergent portion and has a portion with a radius of curvaturecontinuously increasing from upstream to downstream.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic partial longitudinal sectional view of a prior artexhaust nozzle.

FIG. 2 is a schematic partial longitudinal sectional view of an exhaustnozzle according to principles of the invention.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

FIG. 1 shows an exemplary prior art nozzle 30 mounted to an enginestatic ring 31. In this schematicized view, various parts (e.g.,actuators) and details are not shown and may represent known engineeringdetails. The nozzle has an upstream section 32 formed by acircumferential array of upstream flaps 34 (known as convergent flaps)about a nozzle/engine centerline or central longitudinal axis 500. Eachflap 34 extends from an upstream end 35 to a downstream end 36. Eachflap 34 has an interior surface 38 which cooperate to form the interiorsurface of the upstream section 32. A downstream section 40 is formed bya similar circumferential array of downstream flaps 42 (known asdivergent flaps) shown in low mode (solid line) and high mode (brokenline). Each flap 42 extends from an upstream end 44 to a downstream end45 and has an interior surface 46.

In the exemplary embodiment, each downstream flap 42 is hinged to anassociated upstream flap 34 by a hinge 50 coupling the upstream flapdownstream end 36 to the downstream flap upstream end 44 for relativerotation about a hinge axis 502. The hinge 50 permits the articulationof the downstream flap 42 in a range between its high and low modeorientations. Such articulation is driven by aerodynamic pressure forcesacross the combination of the downstream flap 42 and an associatedexternal flap 54.

Each external flap extends from an upstream end 55 to a downstream end56 and has an outboard (exterior) surface 58. The upstream end iscoupled to the static ring structure by a hinge 60 for relative rotationabout a hinge axis 504. The downstream end 56 is coupled to thedownstream end 45 of the flap 42 by a hinge 62 for relative rotationabout a hinge axis 506. The external flap is configured so that its spanbetween axes 504 and 506 may extend and contract (such as by havingtelescoping members). This extendability/contractability permits theaerodynamic forces acting across the divergent/external flap combinationto articulate the flap combination through a range of conditions betweenthe solid line low mode and broken line high mode, with the contractionoccurring from low to high mode and extension occurring in the oppositedirection.

In the exemplary embodiment, in longitudinal section the upstream(convergent) flap interior surface 38 is straight and oriented toconverge toward the axis 500 in a downstream direction so that thecombined interior surfaces of the array of flaps 34 provide a downstreamconvergent, essentially frustoconical, surface with a half angle θ_(I)extending from an inlet 52 at the upstream ends 35 to the downstreamends 36 and hinges 50.

Each downstream (divergent) flap interior surface 46 has, inlongitudinal section, an upstream portion 72 extending downstream fromthe upstream end 44 to a transition 74. The exemplary upstream portion72 is inwardly convex having a substantially uniform radius of curvatureR_(C). A downstream portion 76 between the transition 74 and downstreamend 45 is essentially straight. The location where the surface 72 is ata minimum radius from the axis 500 defines a throat 78 having a radiusR_(T) from the axis. The downstream portions 76, in combination, definea downstream divergent, essentially frustoconical, surface of half angleθ₀ extending from the transition to an outlet/exit 80 at the downstreamends 45. In the exemplary nozzle, the nominal throat radius (and thusthe associated area) may be controlled by an actuation system (notshown) mounted relative to the static ring 31 and which shifts theposition of the transversely-extending axis 502 of the hinge 50 such asby rotating each convergent flap 34 about an axis 509 of a hinge 82 atits forward end 35.

In an exemplary embodiment of the prior art nozzle 30, the inlet radiusR_(I) is 18.8 inches, the angle θ_(i) is 43°, the flap hinge radiusR_(H) is 13.7 inches, and the radius of curvature R_(c) is 3 inches. Inlow mode, the angle θ₀ is 4.40, the throat radius R_(T) is 12.8 inches,the axial longitudinal distance L_(T) between the throat and hinge is1.8 inches, the exit radius R_(E) is 14.4 inches, the hinge-to-exitaxial length L_(E) is 24 inches and the inlet to exit axial length L is30 inches. In the low to high mode transition, the throat shiftsslightly forward along the surface 72 and radially outward with therotation of the divergent flap. The shifted throat radius is shown asR′_(T). In high mode, θ′_(o) is 9°, R′_(T) is 13.0 inches, L′_(T) is 1.7inch and R′_(E) is 16.1 inch.

Various aspects involve the reengineering of the nozzle (e.g., toprovide a drop-in replacement). In an exemplary reengineering, it willlikely be desired to maintain the inlet radius R_(I) for mating with theremainder of the engine. Aerodynamic performance considerations maydictate that other parameters be generally preserved (although withslightly more flexibility). For example, it may be desirable to maintainthe same throat radius R_(T) and exit radius R_(E). It may also bedesirable to reuse the upstream flaps for their configurations, thuspreserving the location of the flap hinge 50.

FIG. 2 shows a reengineered nozzle 130 wherein analogous elements tothose of the nozzle 30 of FIG. 1 are shown with like numeralsincremented by 100. Illustrated elements not discussed separately arenot referenced separately. On each downstream flap 142, the upstreamportion 172 of interior surface 146 has a non-constant radius ofcurvature R_(C1). Along the upstream portion 172, from upstream todownstream the radius of curvature goes from relatively large torelatively small to relatively large. Specifically, in the exemplaryembodiment, an upstreammost portion 190 is straight, thus having aninfinite radius of curvature. At a transition 192 at a downstream end ofthat portion 190, the radius changes abruptly to a value smaller thanR_(C). The radius then increases downstream to a value larger than R_(C)at the transition 174. The increase may be continuous and smooth (e.g.,as in a segment of a parabola or ellipse). In the extreme, the entireflap may be curving at a less than infinite radius (thus eliminating thestraight upstream and downstream portions). Alternatively, only one suchportion may be eliminated. In exemplary embodiments, the non-straightcurving portion intermediate the straight portions has a longitudinalspan of between 5% and 10% of a hinge-to-exit axial length.

In a first exemplary reengineering of the exemplary embodiment of theprior art nozzle 30, the flap hinge position and outlet positions arepreserved, necessitating only a reengineering of the divergent flap andnot the convergent and external flaps.

In a second, more extensive, exemplary reengineering of the exemplaryembodiment of the prior art nozzle 30, the hinge radius R_(H1) is 13.5inch, a slight decrease. The angle θ_(I1) is 44°, a slight increase. Theradius of curvature R_(C1) continuously increases from an upstream valueof 0.5 inch to a downstream value of 8.0 inches. This curvature profilebrings the throat forward relative to the hinge, and, in the exemplaryembodiment, relative to the inlet. In an exemplary low mode, R_(T1) is12.80 inches (relatively unchanged from the baseline), and R_(E1) is14.4 inches (relatively unchanged from the baseline) . θ_(o1) is 4.3°slightly reduced relative to θ_(o). In high mode, R′_(T1) is 12.81inches, R′_(E1) is 16.1 inches, and θ′_(o1) is 8.9°. A greater range ofcurvature change is possible. Exemplary ranges for the low radius ofcurvature are 0.25-1.0 inch, more narrowly 0.25-0.5 inch. The high maybe an exemplary 8.0-14.0 inches, or more.

The increase in hinge radius along with the more radial direction of theflap surface immediately downstream thereof helps hide the hinge fromRADAR. The change in relative position of the throat and hinge alsomakes the throat radius and longitudinal position of the exemplarymodification less sensitive to changes in outlet angle and exit radiusduring mode changes (without changes due to throttling by the actuationsystem). This may better control RADAR cross-section (RCS) during modetransitions by better concealing the flap hinge.

One or more embodiments of the present invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention. Forexample, details of the engine to which any particular nozzle is to beattached will dictate or influence features of the nozzle. Especiallywhen applied as a redesign of an existing nozzle, various features ofthe existing nozzle may be preserved. Accordingly, other embodiments arewithin the scope of the following claims.

1. An exhaust nozzle for a gas turbine engine comprising: an upstreamsection having an interior surface converging in a downstream direction;and a downstream section having an interior surface downstream of theinterior surface of the upstream section, the downstream sectioncomprising a circumferentially arrayed plurality of flaps, each flappivotally coupled to the upstream section for articulation through arange of orientations, wherein: the interior surface of the downstreamsection along each flap has a central longitudinal radius of curvaturethat from upstream to downstream has: at least a first value along afirst portion; at least a second value, less than the first value, andbetween 0.25 inch and 1.0 inch along a second portion; and at least athird value, less than the first value, and between 5.0 inches and 10.0inches along a third portion.
 2. The nozzle of claim 1 wherein saidradius of curvature is: essentially infinite along a fourth portiondownstream of the third portion.
 3. The nozzle of claim 1 wherein saidradius of curvature is: less than infinite along the entire downstreamsection.
 4. The nozzle of claim 1 wherein said radius of curvature is:essentially infinite along the first portion; and continuouslyincreasing from a low of between 0.25 inch and 5.0 inches to a high ofat least 8.0 inches.
 5. The nozzle of claim 4 wherein said continuousincrease occurs over a longitudinal span of between 2.0 inches and 3.0inches.
 6. The nozzle of claim 5 wherein said longitudinal span at leastpartially overlaps the second and third portions
 7. The nozzle of claim4 wherein said continuous increase occurs over a longitudinal spanhaving a length of between 5% and 10% of a longitudinal length of thedownstream section.
 8. The nozzle of claim 1 wherein said range oforientations extends between: a low mode orientation wherein a ratio ofan exit area to a throat area is between 1.05:1 and 1.5:1; and a highmode orientation wherein said ratio is larger than said ratio in saidlow mode orientation and between 1.3:1 and 2.0:1.
 9. The nozzle of claim8 wherein: in the low mode orientation said ratio is between 1.1:1 and1.3:1; and in the high mode orientation said ratio is between 1.4:1 and1.5:1.
 10. The nozzle of claim 8 wherein: between the low and high modeorientations, a throat radius changes by less than 0.5%.
 11. The nozzleof claim 8 wherein: between the low and high mode orientations, a throatradius changes by less than 0.2%.
 12. The nozzle of claim 1 wherein:each flap is pivotally coupled to the upstream section for rotationabout an associated hinge axis, said hinge axis having a first radialdistance from a centerline of the nozzle and said flap having alongitudinal flap length from said hinge axis to an outlet end of saidflap; the downstream section has a throat having a second radialdistance from the centerline and a first longitudinal distance from saidhinge axis; and a ratio of said first longitudinal distance to saidlongitudinal flap length is between 0.05:1 and 0.20:1.
 13. Aconvergent/divergent exhaust nozzle for a gas turbine engine comprising:an upstream section having an interior surface converging in adownstream direction; and a downstream section having an interiorsurface downstream of the interior surface of the upstream section, thesecond portion comprising a circumferentially arrayed plurality offlaps, each flap pivotally coupled to the upstream section forarticulation through a range of orientations, wherein: the interiorsurface of the downstream section along each flap has a centrallongitudinal radius of curvature that from upstream to downstream has:at least a first value along a first portion; at least a second value,less than the first value, and between 0.25 inch and 1.0 inch along asecond portion; and at least a third value, less than the first value,and between 8.0 inches and 14.0 inches along a third portion.
 14. Thenozzle of claim 13 wherein: the radius of curvature is essentiallyinfinite along the first portion; and the radius of curvature isessentially infinite along a fourth portion downstream of the thirdportion.
 15. The nozzle of claim 13 wherein: the first portion extendsfrom an upstream end of the downstream section; the radius of curvatureis essentially infinite along the first portion; the first portion isimmediately upstream of the second portion; the second portion isimmediately upstream of the third portion; and the radius of curvatureis essentially infinite along a fourth portion immediately downstream ofthe third portion and extending to a downstream end of the downstreamsection.
 16. The nozzle of claim 13 used as a replacement for a baselinenozzle having a convergent flap longitudinal radius of curvatureconsisting of: an upstream portion of infinite radius of curvature; adownstream portion of infinite radius of curvature; and an intermediateportion of a single non-infinite radius of curvature.
 17. The nozzle ofclaim 13 used as a replacement for a baseline nozzle and relative tosaid baseline nozzle: reducing relative changes in a throat diameterbetween a low mode and a high mode; having a throat longitudinallycloser to a hinge location; and immediately downstream of the hingelocation the interior surface is more radial in a given condition. 18.An exhaust nozzle for a gas turbine engine comprising: an upstreamsection comprising a plurality of circumferentially arrayed first flapsand having an interior surface converging in a downstream direction; anda downstream section comprising: a plurality of circumferentiallyarrayed second flaps, each hinged relative to an associated one of thefirst flaps; a downstream outlet; and an interior surface downstream ofthe interior surface of the upstream section, wherein a longitudinalprofile of said downstream section interior surface has: a firstportion; a second portion downstream of the first portion; and a thirdportion downstream of the second portion, the second portion having aradius of curvature that is: lower than a radius of curvature of thefirst portion; lower than a radius of curvature of the third portion;and continuously increasing along an axial span.
 19. The nozzle of claim18 further comprising a plurality of circumferentially arrayed thirdflaps, each outboard of and hinged relative to an associated one of thesecond flaps.
 20. The nozzle of claim 18 wherein the radius of curvatureof the second portion varies from an upstream value of between 0.25 inchand 1.0 inch to a downstream value of between 8.0 inches and 14.0 inchesover said axial span of at least 2.0 inches.